Active and stable Pd-catalyst modified by sulfonate-tailed zwitterionic phosphine for hydroxycarbonylation of alkynes free of any additive

Pd-catalyzed hydroxycarbonylation of alkynes with CO and H₂O is a promising alternative for one-step synthesis of α,β-unsaturated carboxylic acids advantageous with 100 % atom-economy, but suffering from rapid catalyst deactivation and unavoidable side reactions like polymerization and hydration while the auxiliary acid-additive is required as a co-catalyst. Herein, free of any auxiliary acid-additive and under mild conditions (0.5 MPa, 60 °C, 3 h), a flexible zwitterionic phosphine of L1 containing a mono-phosphino-fragment and a hydrophilic sulfonate group (–SO₃^-) conferred to Pd(OAc)₂ catalyst efficient performance for hydroxycarbonylation of terminal alkynes, affording the branched α,β-unsaturated carboxylic acids in the yields of 85 ∼ 91 % with 100 % regioselectivity. In addition, the developed L1-Pd(OAc)₂ system was so stable that it could be recycled for 30 runs with well-maintained activity and selectivity, which proved the most active and stable to date under acid-additive-free condition.